This invention is generally directed to toner and developer compositions, and, more specifically, the present invention is directed to toner compositions and processes for the preparation of toner compositions. In embodiments, there are provided in accordance with the present invention in situ processes for the preparation of toner compositions with average volume particle sizes equal to, or less than about 10 micrometers in embodiments without resorting to classification. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and ionography. In an embodiment, the present invention is directed to a process for preparing a toner comprised of resin particles comprised of a nonpolar copolymer resin, a pigment, optionally a charge control agent, and wherein the resin particles have chemically modified outer surfaces and an average diameter of about 1 to 10 micrometers. In embodiments, the process of the present invention comprises preparing an aqueous suspension by agitating and subsequently polymerizing a mixture of nonpolar olefins such as styrene and butadiene in an aqueous medium containing a mixture of a free radical initiator, a surfactant, a pigment, and polymerizing the mixture by heating to form nonpolar olefinic resin particles suspended in water comprised of, for example, poly(styrene-butadiene) of from about 3 to about 10 micrometers in diameter; chemically modifying the resin particle resin particle surface with, for example, chlorine gas to transform the olefinic resin present on the outer surface of the toner particle to, for example, a chlorinated poly(styrene-butadiene) species poly(styrene-butadiene-dichloro butene); and optionally isolating the toner particles by centrifuging, washing and drying. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic imaging and printing processes, including color processes.
In an embodiment of the instant invention a process for the preparation of nonpolar toner particle compositions is disclosed comprising: preparing an organic phase comprised of a first nonpolar olefinic monomer, a second nonpolar diolefinic monomer, a pigment, a free radical initiator, and optionally a charge control agent; adding the organic phase to an aqueous phase containing at least one surfactant; shearing the organic phase into the aqueous phase to form a microdroplet suspension of the organic phase dispersed in the aqueous phase; heating and polymerizing the microdroplets in the suspension to form nonpolar olefinic resin particles; halogenating the nonpolar olefinic resin particle mixture to form nonpolar toner particles having a halopolymer resin outer surface or encapsulating shell; and optionally isolating the surface halogenated nonpolar toner particles. Flow additives to improve flow characteristics may then optionally be employed such as Aerosils or colloidal silicas, and the like, of from about 0.1 to about 10 percent by weight of the toner.
In another embodiment the present invention is directed to a process for the preparation of a toner composition comprising: milling a mixture of a polymeric resin a pigment and optionally an organic solvent and a charge control additive; homogenizing the mixture in an aqueous solution containing a surfactant or mixture of surfactants; heating the homogenized mixture obtained to form toner particles; halogenating the toner particles to form toner particles having a halopolymer resin outer surface or encapsulating shell; and optionally isolating the surface halogenated toner particles.
In yet another embodiment the present invention is directed to a process for the preparation of a toner composition comprising: preparing a suspension by shearing into a water containing mixture of a surfactant, a first nonpolar olefinic monomer, a second nonpolar olefinic monomer, a thermoplastic resin preferably as a fine powder, a pigment and optionally a charge control agent; polymerizing the suspension by heating to form toner resin particles; halogenating the toner particles to form toner particles having a halopolymer resin outer surface or encapsulating shell; and optionally isolating the surface halogenated toner particles, or toner composition.
In still yet another embodiment the present invention is directed to a process for the preparation of a toner composition comprising: preparing a suspension by shearing into water containing a mixture of a surfactant, a thermoplastic resin dissolved in a low boiling organic solvent, a pigment and optionally a charge control agent; heating the suspension; removing the organic solvent thereby generating a suspension of particles in water; halogenating the suspended particles to form toner particles having a halopolymer resin outer surface or encapsulating shell; and optionally isolating the surface halogenated toner particles.
In reprographic technologies, such as xerographic and ionographic devices, toners with small average volume diameter particle sizes of from about 5 microns to about 20 microns are utilized. Moreover, in some xerographic technologies, such as the high volume Xerox Corporation 5090.TM. copier-duplicator, high resolution characteristics and low image noise are highly desired, and can be readily attained utilizing small sized toners with average volume particle of less than 11 microns and preferably less than about 7 microns and with narrow geometric size distribution (GSD) of less than about 1.4 and preferably less than about 1.3. Additionally, in some xerographic systems wherein process color is required such as pictorial color applications, small particle size colored toners of less than 9 microns and preferably less than about 7 microns are highly desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper due to the high fusing temperatures of from about 130.degree. to 160.degree. C. applied to the paper from the fuser. Where only one layer of toner is present such as in black or highlight xerographic applications, the amount of moisture driven off during fusing is reabsorbed proportionally by paper and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step inhibits the paper receiving sheet from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. Since surface area of the toner particle is inversely proportional to toner particle size, it is preferable to use small toner particle sizes of less than 9 microns and preferably less than about 7 microns and with higher pigment loading such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image and resulting in a thinner plastic toner layer onto paper after fusing, and hence, minimizing or avoiding paper curling. Toners prepared in the present invention with lower fusing temperatures such as from about 100.degree. to about 140.degree. C. help to avoid paper curl. Lower fusing temperatures minimize the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, high gloss is necessary, as well as high projection efficiency properties with transparency images.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 7 microns to about 20 microns and with broad geometric size distribution of from about 1.4 to about 1.7. In such processes it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 are attained. However, in the aforementioned conventional process, low toner yields after classifications may be obtained and are dependent on the average volume particle sizes of said toner. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention in embodiments, small average particle sizes of from about 3 microns to about 9, and preferably 7 microns are attained without resorting to classification processes, and wherein high toner yields are attained such as from about 90 percent to about 98 percent in embodiments. Additionally, toners prepared by conventional processes must not readily aggregate or block during manufacturing, transport or storage prior to use in electrophotographic systems and must exhibit low temperature fusing properties in order to minimize fuser energy requirements. Accordingly, conventional toner resins are restricted to having glass transition temperatures of greater than about 55.degree. C. and preferably of about 60.degree. C. to satisfy caking or blocking requirements. Toner caking or blocking is known in the art and refers to the minimum temperature necessary for toner aggregation to occur over an extended period of time, such as from about 24 hours to 48 hours. The caking or blocking temperature requirement of a toner should be greater than about 55.degree. C. and preferably greater than about 60.degree. C., in order to avoid toner aggregation in storage or use prior to fixing a powdered toner image to a receiver sheet. This blocking requirement restricts the toner fusing properties, that is minimum fix temperature, of from about 135.degree. C. to about 160.degree. C. In process color or pictorial applications, wherein low paper curl is a requirement, low toner fusing properties are desired such as less than about 140.degree. C. and preferably less than 110.degree. C. such that moisture evaporation or removal from paper is minimized or preferably avoided. With the toners of this invention, the toners fuse at lower temperatures than conventional toners, such as from about 110.degree. to about 150.degree. C., thereby reducing the energy requirements of the fuser and more importantly resulting in reduced moisture being driven off from the paper during fusing, and hence lowering or minimizing paper curling. For the toners of this invention, the blocking and fusing properties of the toners are disintegrated or separated by the chemical surface process of halogenating the toner surface. During the process for the preparation of the toner of this invention, the polymerized resin or resins as toner particles such as poly (styrene-butadiene) exhibit a glass transition temperature of from about 40.degree. C. to about 50.degree. C. and thermal properties amenable to achieve low fusing properties such as from about 110.degree. C. to about 140.degree. C. In the optional halogenation or chlorination step, the outer surface of the toner resin particle surface is chemically transformed from poly(styrene-butadiene) to, for example, chlorinated poly(styrene-butadiene) such that the outer surface of the toner resin particle has a glass transition of from about 55.degree. C. to about 60.degree. C. necessary for the blocking requirement. This latter chemical surface treatment step allows one to separate toner blocking requirements from fusing requirements and results in low fusing toners of from about 110.degree. C. to about 140.degree. C. which are necessary to minimize or eliminate paper curling. That is, by lowering the fusing temperature range to about 100.degree. to 140.degree. C. a reduction or elimination in paper curl is achieved. In addition, by the toner particle preparation process of this invention, small particle size toners of from about 3 microns to about 7 microns are prepared with high yields as from about 90 percent to about 98 percent by weight of all toner starting material ingredients.
Additionally, other processes such as and including encapsulation, coagulation, coalescence, suspension polymerization, or semi-suspension and the like, are known, wherein the toners are obtained by in situ one pot methods. Moreover, encapsulated toners are known wherein a core comprised of pigment and resin is encapsulated by a shell, and wherein the toner melt rheological properties are separated wherein a core material provides low fusing properties such as from about 100.degree. to 125.degree. C. and an encapsulating shell provides necessary blocking properties for particle stability prior to fusing. However, it is known that encapsulated toners do not provide high gloss due to high surface tension, high glass transition and high melting temperatures of the shell, and also result in poor projection efficiency due to the difference in refractive index between the shell and core resulting in light scattering. Other in situ toners prepared by suspension, coagulation, coalescence, are known, wherein the toners are comprised of substantially similar compositions to conventional toners with, in some cases, having surfactants or surface additives on the toner surface prepared by various processes. Although, these latter aforementioned toners are amenable to high gloss, high projection efficiency, and small particle size toners, their fusing performances are restricted to the thermal properties of the bulk toner, such as glass transition (T.sub.g), in that the toners must satisfy blocking requirements and hence are restricted to glass transitions of above 55.degree. C. and therefore fusing temperatures of from about 135.degree. to about 160.degree. C., and have inferior paper curl properties for process color applications. By the processes of the present invention, toner melt rheological properties are separated in that a heterogeneous surface halogenation chemical process increases the glass transition of the outer surface resin of the toner particle of from about 45.degree. to 55.degree. C. to about 55.degree. to 60.degree. C. or greater, hence providing required blocking properties and low fusing temperatures of from about 110.degree. C. to about 140.degree. C. necessary for minimizing or avoiding paper curling.
The following patents, the disclosures of which are entirely incorporated herein by reference, are also mentioned.
Illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, see, for example, columns 4 and 5. In column 7 of the '127 patent it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization as indicated in column 3. Additionally, note column 9, line 50 to 55, wherein polar monomers such as acrylic acid in the emulsion resin is necessary, and note Comparative Example 1, column 9, lines 50 to 55 wherein toner preparation is not obtained without the use of a polar group such as acrylic acid. Unlike the '127 reference, the present invention is directed to improved processes wherein suspended monomers or polymers, or dissolved polymer resins, or resultant composite resin particles do not contain acidic or basic groups, and toner particles are obtained without the use of polar acidic groups such as acrylic acid, thereby reducing toner humidity sensitivity. Additionally, with processes of the instant invention, halogenation, for example, chlorination of the outer surface of the toner particles provides an improvement in blocking characteristics, and hence enhances the minimum fix temperature properties of the toner.
Illustrated in U.S. Pat. No. 4,797,339, is a toner composition comprised of an inner layer comprising a resin ion complex having a coloring agent, a charge enhancing additive and pigment dispersed therein, and an outer layer containing a flowability imparting agent. Note column 2 and 3, wherein the ion complex resin is comprised of an acidic emulsion copolymer resin and basic emulsion resin comprised of styrene acrylates containing acidic or basic polar groups similar to the '127 patent.
U.S. Pat. No. 4,983,488 discloses a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100 micrometers in diameter, and particularly 3 to 70 micrometers in diameter, are obtained. It is also indicated in column 4, lines 60 to 65, that the glass transition of the emulsion resin should be above 50.degree. C., and when the glass transition is too low, caking resistance, that is resistance to blocking, tends to decrease and if the glass transition is too high the fixing property tends to be poor. The toners of the present invention differ from the '488 reference toners in that the process is simple and does not utilize coagulating agents. Moreover, resins or resin blends with relatively lower glass transition of about 40.degree. to 45.degree. C. are used, and resistance to caking is avoided by the halogenation process of the toner surface wherein the glass transition is raised to about 50.degree. to about 55.degree. C., hence caking, blocking or undesired aggregation of toner particles is avoided and low fixing temperatures are maintained as well as excellent triboelectric characteristics, high gloss, and low humidity sensitivity.
Documents disclosing toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014; 4,394,430; and 4,560,635 which illustrates a toner with a distearyl dimethyl ammonium methyl sulfate charge additive. These toners are prepared, for example, by the usual known jetting, micronization, and classification processes. Toners obtained with these processes generally possess a toner volume average diameter of form between about 10 to about 20 microns and are obtained in yields of from about 85 percent to about 98 percent by weight of starting materials without classification procedure.
Copending application U.S. Ser. No. 07/767,454 (D/90156), filed Sep. 30, 1991, the disclosure of which is totally incorporated herein by reference, discloses an in situ suspension process for preparing a toner comprised of a core comprised of a resin, pigment and optionally charge control agent and coated thereover with a cellulosic material. Also, in U.S. Pat. No. 5,278,016 (D/90514), filed May 6, 1991 entitled `Toner Compositions`, the disclosure of which is totally incorporated herein by reference, there is illustrated low melt toner particles prepared by conventional comminution processes that are subsequently halogenated to form encapsulated toner particles with a higher melting halopolymer shell. U.S. Pat. No. 5,278,020 (D/92097), filed Aug. 28, 1992, the disclosure of which is totally incorporated herein by reference, discloses a toner composition and processes for the preparation thereof comprising, for example, the steps of: (i) preparing a latex emulsion by agitating in water a mixture of a nonionic surfactant, an anionic surfactant, a first nonpolar olefinic monomer, a second nonpolar diolefinic monomer, a free radical initiator and a chain transfer agent; (ii) polymerizing the latex emulsion mixture by heating from ambient temperature to about 80.degree. C. to form nonpolar olefinic emulsion resin particles of volume average diameter from about 5 nanometers to about 500 nanometers; (iii) diluting the nonpolar olefinic emulsion resin particle mixture with water; (iv) adding to the diluted resin particle mixture a colorant or pigment particles and optionally dispersing the resulting mixture with a homogenizer; (v) adding a cationic surfactant to flocculate the colorant or pigment particles to the surface of the emulsion resin particles; (vi) homogenizing the flocculated mixture at high shear to form statically bound aggregated composite particles with a volume average diameter of less than or equal to about 5 microns; (vii) heating the statically bound aggregate composite particles to form nonpolar toner sized particles; (viii) optionally halogenating the nonpolar toner sized particles to form nonpolar toner sized particles having a halopolymer resin outer surface or encapsulating shell; and (ix) isolating the nonpolar toner sized composite particles.
Additionally, U.S. Pat. No. 4,876,313, discloses an improved core and shell polymers having an alkali-insoluble core and an alkali-soluble shell which polymers are prepared by emulsion polymerization of the core-shell polymers utilizing compounds which chemically graft the core and shell polymers together.
There remains a need for black or colored toners having small particle sizes of less than or equal to 7 microns in volume diameter. Furthermore, there is a need for colored toner processes wherein the toner synthetic yields are high, such as from about 90 percent to about 100 percent while avoiding or without resorting to classification procedures. In addition, there remains a need for black and colored toners that are non-blocking, such as from about 55.degree. to about 60.degree. C., of excellent image resolution, non-smearing and of excellent triboelectric charging characteristics. Moreover, there remains a need for black or colored toners with: low fusing temperatures, of from about 110.degree. C. to about 150.degree. C.; of high gloss properties such as from about 50 gloss units to about 85 gloss units; of high projection efficiency, such as from about 75 percent to about 95 percent efficiency or more; and which toners enable developed images with minimal or no paper curl.